ByDonald Kirk, CorrespondentJuly 26, 2010

Fighter jets prepare to take off from the USS George Washington as South Korean navy's landing ship Dokdo Ham, top, passes by during joint military exercises between the U.S. and South Korea in South Korea's East Sea on July 26.

American and South Korean ships and planes fired on imaginary North Korean submarines Monday as four days of joint exercises reached the half-way mark with no sign of North Korea doing anything to spoil the war games – yet.

US and South Korean officials are not quite prepared to say they have called the North Koreans’ bluff by ignoring its threats of a strong – even nuclear – response to the exercises. But most analysts are convinced that the North had no intention of challenging the might of the air and naval forces amassed off South Korea’s east coast.

Kim Tae-woo, long-time analyst of North Korean intentions at the Korea Institute for Defense Analyses, doesn't think North Korea is ready to explode a nuclear device for the third time. “A long-range missile test is more possible,” he says. “That’s easier. We should be prepared.”

As some 20 ships and 200 aircraft zigzagged through the seas and skies about 70 miles off South Korea’s coast, the North Korean media kept up a steady drumbeat of denunciations reminiscent of the North’s diatribes during previous US-South Korea military exercises.

The difference this time was that the stakes have risen sharply since the sinking of South Korean navy corvette the Cheonan in March in which 46 sailors died. A South Korean investigation, which included the views of experts from the US, Britain, Australia, and Sweden, blamed a North Korean midget submarine for firing the torpedo that split the Cheonan in two and sunk it in minutes.

North Korea denies any role in the attack.

Divide and conquer strategy?

North Korea’s strategy of denial appears to many analysts to have sharpened the divisions among the nations that have participated in recent years in so-called six-party talks on the North’s nuclear program. North Korea has said it now wants to return to the talks, last held in Beijing in December 2008, but “we have a crack among the parties,” says Professor Kim Sung-han. China and Russia support the North, he says, while the US and Japan support the South.

On a more practical level, “Operation Invincible Spirit,” as the current war games are called, has provided an opportunity for American and South Korean forces to perfect coordination on some of their most sophisticated weaponry in the biggest joint exercises conducted by the two allies in more than 30 years.

The US commander in Korea, Gen. Walter “Skip” Sharp, said the exercises “send a clear message to North Korea that its aggressive behavior must stop” and that the US and South Korea “are committed to enhancing our combined defensive capabilities."

As warplanes roared from the deck of the nuclear-powered aircraft carrier the USS George Washington, at 98,000 tons one of the biggest in the US navy, US and South Korean destroyers and at least one South Korean submarine cruised surrounding waters. For the first time, US Air Force F-22 raptors also joined the games, taking off with scores of other aircraft from the major US base at Osan.

Aside from symbolic significance, the focus on anti-submarine warfare showed the frustration over countering future submarine attacks. A South Korean military spokesman said the exercises Monday were “aimed at better detecting intrusions by an enemy’s submarines and attacking them.”

North Korea’s national defense commission, the center of power for leader Kim Jong-il, the commission chairman, greeted the war games with a blitzkrieg of invective ranging from a warning of “retaliatory sacred war” to the threat of deploying a “powerful nuclear deterrent.”

The strong language inspired derisive rejoinders from analysts mingled with concern about what it meant in terms of North Korea’s ambitions as a nascent nuclear power.

“They feel they cannot allow this [military exercise] to happen without this reaction,” says Han Sung-joo, who has served previously as South Korea’s foreign minister and ambassador to Washington. “I don’t think anything will happen in the next few days.”

Analysts see the allusion to “nuclear deterrence,” however, as indicating North Korea’s ambitions for its nuclear program. North Korea has twice conducted underground nuclear tests, first in October 2006 and again in May of last year, and is believed to have enough weapons-grade plutonium for between six and a dozen warheads.

“They might want to use this occasion as an opportunity or excuse to do something with their nuclear program,” says Mr. Han. “They can conduct another nuclear test or do something with their missiles.” North Korea has successfully built short and medium-range missiles and in April of last year test-fired a long-range missile capable of reaching the US west coast.

The China factor

In any case, China’s refusal to support the United States and South Korea in blaming North Korea for the attack on the Cheonan is assumed to have emboldened the North. China instead went along with a watered-down statement issued by the UN Security Council that noted the investigation and condemned the attack but did not hold North Korea responsible for it.

“One element here is China,” says Han Sung-joo. The North Koreans “probably think they have managed to bring China to their side. They are trying to make full use of what they consider to be China’s backing.”

Analysts say that the view that China will always back the North may also lead to another unexpected attack on the South. “They usually try to do the thing that were not expected,” says Mr. Han, but he doubts if North Korea “can do anything that will force us to take retaliatory measures.”

Mr. Kim, from the Korea Institute for Defense Analyses, agrees. “They cannot do anything against our exercises,” he says.

“They may plan something against South Korea, and they practice nuclear blackmail.”